This project is studying the roles of sterol carrier protein 1 (SCP1) and sterol carrier protein 2 (SCP2) in cholesterol metabolism. SCP1 is required for the enzymatic conversion of squalene to lanosterol by liver microsomal membranes. SCP2 is required for the enzymatic conversion of lanosterol to cholesterol by liver microsomes. In addition, SCP2 also participates in reactions which utilize cholesterol, e.g., the conversion of cholesterol ester. We also have obtained evidence which supports the concept that SCP 2 participates in the intracellular transfer of cholesterol.